Scientist often use which are programs that combine what is known about atmospheric circulation

General circulation model.

Explanation:

A general circulation model (GCM) is a type of climate model that employs a mathematical model of the general circulation of a planetary atmosphere or ocean. GCM uses the Navier–Stokes equations on a rotating sphere with thermodynamic terms for various energy sources (radiation, latent heat). These equations are the basic equations for computer programs used to simulate the Earth's atmosphere or oceans.

The missing word is Computer Based Climate Models.

Explanation:

Computer-Based Climate Models are simply software which uses data collected about atmospheric conditions, air circulation, ocean circulation, interactions between weather elements and various climatic cycles to predict climate and weather.

These are often used by Meteorologists. Meteorologists are simply scientists who study and predict climate and weather.

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the results is a decrease in air temperature with an increase of altitude.

explanation:

d. air pressure decreases as altitude increases.